Uterine disease is an extremely common factor affecting the quality of life and morbidity/mortality of the human female. Each year, more than 35,000 women in the US are diagnosed with endometrial cancer;and endometriosis affects up to 15% of reproductive aged women and often results in infertility. Further, inadequate preparation of the uterine lining during early gestation is thought to contribute to recurrent spontaneous pregnancy loss. It is clear that stem cells coordinate developmental and tissue renewal processes during the construction and maintenance of most organs. Yet there are almost no studies of stem cells in the development of the uterus, an organ that undergoes perhaps the most extensive proliferative changes and developmental remodeling in adult mammals. We hypothesize that endogenous endometrial stem/progenitor cells play a functional role in the cyclic changes within the uterus. Our experimental efforts involving bone marrow transplantation, peripheral blood cell infusions and parabiosis have collectively ruled out the likelihood that bone marrow contributes stem cells to uterine tissue architecture as has been suggested by others. Pulse- chase experiments using H2B:GFP transgenic mice and fate mapping studies revealed the identity of long-term label retaining cells (LRC) in the glandular epithelium and stromal compartment nearest the stromal:myometrial interface. A mouse model of endometrial regression and regeneration reveals that despite complete loss of the luminal epithelium following uterine decidualization, residual glandular tissue is sufficient to completely replace all epithelial tissue, an event that occurs in the absence of ovarian derived steroid hormones. Ongoing studies involving isolation and in vivo transplantation will test the stem cell activity of these putative stromal and epithelial adult stem cells. The long term goal of this proposal is to establish a framework with which to build upon as we begin to understand how endometrial stem cells contribute to normal uterine development and fertility, as well as to uterine diseases like endometriosis and endometrial cancer when stem cell function goes awry. PUBLIC HEALTH RELEVANCE: Dysfunction of the uterus is a common factor affecting fertility, the quality of life, and morbidity/mortality of the human female. Each year, more than 35,000 women in the United States are diagnosed with endometrial cancer (fourth most frequent among women), and endometriosis, another debilitating uterine disease that often results in severe pelvic pain and infertility, affects up to 15% of all reproductive aged women. Recurrent pregnancy loss, occurring in an estimated 25-60% of all mammalian conceptions, is thought to occur in part because of faulty preparation of the uterine lining during early pregnancy. Our understanding of these uterine pathologies, and in particular their etiology, is at best limited. Normal uterine function, and thus successful pregnancy, is dependent on normal cycles of endometrial growth, differentiation, regression (menses) and regeneration. We hypothesize that stem cells are responsible for maintenance of this uterine cycle and have proposed to isolate and characterize endometrial stem cells. The long-term goal of our proposed studies will be to demonstrate a causal link between faulty uterine stem cell function and gynecologic pathologies that impact negatively on fertility and quality of life in women.